1. Field of the Invention
The present invention relates to a thin film magnetic head generally utilized to write magnetic information data in a magnetic storage device such as a hard disk drive (HDD), for example.
2. Description of the Prior Art
A so-called single pole head is generally employed in a magnetic storage device based on perpendicular recording. The single pole head comprises a magnetic pole major layer or yoke layer and a tip magnetic layer or primary magnetic pole layer. Such a single pole head is disclosed in “Advanced Probe Head for Perpendicular Recording” Liu et al., IEEE Transactions on Magnetics, Jul. 2002, vol. 38 No. 4, p 1647-1651, for example. A magnetic field is applied to the backing layer of a magnetic recording disk from the front end of the primary magnetic pole layer. Magnetic flux is introduced to the primary magnetic pole layer from the yoke layer.
A primary magnetic pole tip region is defined in the primary magnetic pole layer in a section adjacent the medium-opposed surface of a head slider. The primary magnetic pole tip region is designed to extend from the medium-opposed surface toward a coil. The primary magnetic pole tip region maintains a constant lateral width. The primary magnetic pole layer includes a section having an increased lateral width behind the rear end of the primary magnetic pole tip region. Since the thickness of the primary magnetic pole layer is set considerably smaller than that of the yoke layer, the constant lateral width of the primary magnetic pole tip region can be established at a higher accuracy. The width of recording tracks can thus be reduced on the magnetic recording disk.
However, the sectional area of the primary magnetic pole layer remarkably gets reduced at the entrance or rear end of the primary magnetic pole tip region. The reduced sectional area of the primary magnetic pole layer induces saturation of magnetic flux. As a result, the leakage of the magnetic field is made less from the front end of the primary magnetic pole tip region. If the length of the primary magnetic pole tip region can sufficiently be reduced in the primary magnetic pole layer, the primary magnetic pole layer can be prevented from suffering from degradation of the magnetic field leaking from the front end of the primary magnetic pole tip region.
Ion milling process is usually employed to form the aforementioned primary magnetic pole tip region in the primary magnetic pole layer. In this case, a photoresist film is formed on a magnetic material layer so as to define the shape of the primary magnetic pole layer. The magnetic material layer is removed around the photoresist film.
Since the lateral width of the primary magnetic pole layer gets remarkably increased behind the rear end of the primary magnetic pole tip region, the photoresist film tends to hinder the irradiation of ions at the rear end of the primary magnetic pole region. The magnetic material layer cannot sufficiently be removed near the rear end of the primary magnetic pole tip region. The primary magnetic pole tip region thus suffers from an increased lateral width at a section near the rear end. The constant lateral width cannot be established in the primary magnetic pole tip region. If the length of the primary magnetic pole tip region is reduced in the aforementioned manner, the dimensional accuracy of the primary magnetic pole tip region gets degraded at the medium-opposed surface.